DRO: How do you know when to change blower speed? You’re going off Density Altitude?

DW: Let’s just say for 2,000 feet D.A. you’re 40% over, at 1,500 feet you want to be about 35% over, and we have it worked out in 1% increments.

DRO: So how much does a .001” head gasket change effect the boost? Does it show up on the boost pressure recording?

DW: You can’t see that in boost, but I have a formula that I use that says X-amount of head gasket thickness is equal to 1% of blower, or 1% of nitro is equal to X% of blower drive or X amount of compression ratio change.

DRO: Do you change nitro percentage very much, or do you run right at 90% all the time?

DW: We stay pretty close, just over 89%, on this particular car.

DRO: When do you change nitro percentage? Last minute, in the lanes?

DW: We don’t. We just do overdrive last minute. I see guys doing it, and it must make a difference and they must have a formula for that also. I think what guys do is go up there a little bit over-tuned and then knock it down to the exact tune-up right when they run, with the nitro percentage. If they go up there and the altitude is 2,000 feet, and it drops to 1,850 right before they run, they’ll get rid of that extra power by dumping in some methanol right at the last second, to keep the power right where they want it. You’ll see them dump it in, and it’s tiny amounts.

DRO: How about compression heights on the pistons? Are they all the same, or are they shorter in the front because of the way the rotors are curved and the way they run together it actually forces more air to the front? Are the manifolds good enough at distributing an equal amount of air to each cylinder that they can all be the same, or is there more to it than that?

DW: They’re different. We try to get all the jetting the same so each cylinder makes the same amount of power, then we adjust the compression ratio to keep it from detonating. So, let’s say number one cylinder might be 6.2 to 1 and number five cylinder might be 7 to 1. That’s an extreme, but it can happen that way. Cylinders one and five are the two furthest apart in the engine when it comes to compression. Five is just barely along for the ride most of the time, for whatever reason, and one being the workhorse of the engine, which is typical of almost every Hemi I’ve ever worked on. Since we can’t run individual cylinder timing, we have to change piston compression height, or rod length, however you want to do it.

DRO: Have you ever had a nice, clean run and when you came back and tore it down, the motor was spotless inside and you could rerun it? Most people assume that it’s “normal” for a nitro motor to eat itself up every pass.

DW: Yeah, there are times when the motor looks really nice, but the bearings need to be changed. They get hammered and the oil pressure wouldn’t be up to where it needs to be. Everything has a cycle life and only gets so many runs before it’s changed out, so we’re always on top of that.

(Wayne Smothers photo)

DRO: How about fuel pump flow? I know you guys flow your own pumps, how fast do they wear out?

DW: It’s not too big of a deal anymore. Fuel pumps now-a-days, with CNC machining and the great coatings out there, will go half a season pretty easy. Obviously, when it’s first put together it’s a little bit better, and then it just drops the flow down a little bit and when it sets, it’ll pretty much make nearly a whole season anymore. That’s nice. It’s one of those things that’s come along through the years, along with rear ends. You remember back in the day, all we did was work on rear ends. Now about every 50 runs we need to work on it.

DRO: What kind of RPM does the motor go to at the hit of the throttle, where’s it at half track, and where’s it at the 1,000-foot stripe?

DW: It idles at 2,500 RPM, then when we first hit the throttle it goes right to 8,500 RPM, comes down to about 7,000 RPM when the clutch is engaging and then once the output shaft goes one to one with engine speed and there’s no more slippage between the engine and clutch, it runs right back up to 8,000 RPM.